The invention concerns a fastening element for the mounting of insulating strips and/or plates on a solid substructure with a large surface washer and a tube-shaped extension, for the penetration, the guidance, and the mounting of a fastener, which penetrates into the solid substructure.
Such fastening elements are utilized for the mounting of insulating materials on solid backing, as for example for the mounting of insulating plates on roofs. If materials must be transported onto the roof, it can happen that, for example, a worker steps onto a washer or in its close vicinity, or that a vehicle or tool is moved over the washer. Such locally limited forces can cause the free end of the fastener to penetrate through the applied insulation material, or that the washer penetrates the roof shingles, which are attached to the insulation material. Another variation has been suggested, in which a tube-shaped extension is arranged on the relatively large-surface washer, into which a screw is inserted. The head of this screw lies in this case within the tube-shaped extension and is recessed relatively deeply compared to the upper side of the washer, in which the necessary length of the screw is shortened considerably. The thickness of the insulation material can become a negligible factor because of the interaction between the length of the tube-shaped extension and the length of the screw. In connection with this, it already has been suggested to produce the washer and the tube-shaped extension from two separate parts. In both known variations, the possibility exists that the fastening element can be shortened in a telescoping manner during application of the corresponding load, which means, for example, if a person steps on the washer.
One disadvantage in those known variations is that a number of fasteners with different lengths, which usually means the length of the screws, is necessary depending on the thickness of the insulating strips and/plates and especially with different thicknesses of the insulating strips on the roof. This is necessary because the head of the screw must adjoin the base of the inner space of the tube-shaped extension and the tube-shaped extension and the washer must be pressed against the upper side of the insulating strip. If it does not matter how far such a screw is inserted into the solid substructure, this becomes a negligible factor. If the solid substructure consists, for example, of concrete plates or wood with a visible sheeting, these screws cannot be inserted too deeply into the solid substructure.